The replication of duplex DNA requires the formation of single stranded DNA in order to support Watson-Crick base pairing of entering nucleotides in the synthesis of daughter strands. DNA helicases are enzymes which lead to the unwinding of duplex DNA and are found at the replication fork. The long-term objective of this proposal is to identify and characterize DNA helicases that are important in the replication of DNA. The proposal includes the identification, isolation and characterization of DNA helicases that are dependent on the human DNA binding protein for their activity, The three subunit human DNA binding protein is the only binding protein which supports the replication of DNA containing the SV40 origin. This binding protein was also shown to be required for the repair of alkylated or ultraviolet damaged DNA. The replication of Bovine Papilloma virus DNA in vitro by mouse cell free extracts depends upon the viral encoded proteins El and E2. The El protein has been shown to contain DNA helicase activity and binds to the minimal BPV origin of replication. We plan to investigate the mechanism by which the replication of this DNA is regulated. We shall examine the cell cycle control of the unwinding reaction dependent on the BPV core origin catalyzed by the El protein. The regulation of DNA replication is of considerable importance in normal cells. The information derived from the studies described here may contribute to our knowledge of how cancer cells escape this control.